JP4187653B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and is particularly characterized in that the non-aqueous electrolyte is improved to improve the safety of the non-aqueous electrolyte secondary battery.

  In recent years, non-aqueous electrolyte secondary batteries using non-aqueous electrolyte and utilizing lithium oxidation and reduction have been used as one of the new secondary batteries with high output and high energy density. .

Here, in such a non-aqueous electrolyte secondary battery, as a non-aqueous electrolyte, generally, a solute composed of a lithium salt such as LiBF ₄ or LiPF ₆ is dissolved in an organic solvent such as ethylene carbonate or diethyl carbonate. Is used.

  However, organic solvents such as those used in non-aqueous electrolytes are flammable and may burn during abnormal operations such as overcharging. For this reason, a protection circuit is conventionally provided to prevent overcharging. As a result, there are problems such as high costs.

  This invention makes it a subject to solve the above problems in a nonaqueous electrolyte secondary battery. That is, the present invention improves the nonaqueous electrolyte in the nonaqueous electrolyte secondary battery, does not burn even during abnormal operation such as overcharge, and can be used safely without providing a protective circuit or the like. An object is to provide an electrolyte secondary battery.

In the present invention, in a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, the negative electrode used is a copper foil having a roughened surface and a silicon thin film formed thereon, and has a melting point. A room temperature molten salt composed of a quaternary ammonium salt of 60 ° C. or lower, LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN ( Using a non-aqueous electrolyte containing at least one lithium salt selected from CF ₃ SO ₂ ) (COCF ₃ ), trimethylpropyl is added to a room temperature molten salt composed of a quaternary ammonium salt having a melting point of 60 ° C. or lower. Ammonium bis (trifluoromethylsulfonyl) imide, trimethyloctylammonium bis (trifluoromethylsulfonyl) imide, trimethylallylammonium bi (Trifluoromethylsulfonyl) imide, trimethylhexylammonium bis (trifluoromethylsulfonyl) imide, trimethylethylammonium-2,2,2-trifluoro-N- (trifluoromethylsulfonyl) acetamide, trimethylallylammonium-2 2,2-trifluoro-N- (trifluoromethylsulfonyl) acetamide, trimethylpropylammonium · 2,2,2-trifluoro-N- (trifluoromethylsulfonyl) acetamide, tetraethylammonium · 2,2,2-trimethyl At least selected from fluoro-N- (trifluoromethylsulfonyl) acetamide, triethylmethylammonium-2,2,2-trifluoro-N- (trifluoromethylsulfonyl) acetamide We had to use a one.

  When a non-aqueous electrolyte containing a room temperature molten salt having a melting point of 60 ° C. or lower and a lithium salt is used as in the non-aqueous electrolyte secondary battery in the present invention, lithium ions are converted into positive and negative electrodes by the lithium salt. It is possible to charge and discharge by moving between. In addition, the above room temperature molten salt is a liquid consisting only of ions and has no vapor pressure and is incombustible. Therefore, it does not decompose or burn even during abnormal operations such as overcharging, and oxygen It does not burn even with radicals and can be used safely without providing a protective circuit or the like. In addition, when lithium salt is added to room temperature molten salt as mentioned above, it is thought that the melting | fusing point falls from melting | fusing point of 2 types of salts independently, and these are kept in a liquid state.

Here, the above room temperature molten salt needs to be liquid in a wide temperature range with lithium salt mixed, and generally used if it is liquid in the range of -20 ° C to 60 ° C. It is desirable that the conductivity be 10 ⁻⁴ S / cm or more. In addition, the room temperature molten salt described above preferably has a low reduction potential, but preferably has a noble oxidation potential, and the operating potential of the negative electrode capable of inserting and removing Li ions is generally 0.5 to 0 V (vs. since a Li / Li ^+), the reduction potential is desirably less than 0V (vs.Li/Li ^+), but the oxidation potential good is higher, considering that at the time of overcharge, 5V (vs it is desirably .Li / Li ⁺⁾ or more, and more preferably 5.5V (vs.Li/Li ⁺⁾ or more.

And, as such room temperature molten salt, the above trimethylpropylammonium · bis (trifluoromethylsulfonyl) imide ^{_{(CH 3) 3 N + (}} C 3 H 7) N - (CF 3 SO 2) 2, trimethyl octyl ammonium bis (trifluoromethylsulfonyl) imide ^{_{(CH 3) 3 N + (}} C 8 H 17) N - (CF 3 SO 2) 2, trimethyl allyl ammonium bis (trifluoromethylsulfonyl) imide _{(CH 3) 3 ^{N + (Allyl) N - (}} CF 3 SO 2) 2, trimethyl hexyl ammonium bis (trifluoromethylsulfonyl) imide ^{_{(CH 3) 3 N + (}} C 6 H 13) N - (CF 3 SO 2) 2, Trimethylethylammonium 2,2,2-trifluoro-N- (trifluoro Methylsulfonyl) acetamide ^{_{(CH 3) 3 N + (}} C 2 H 5) (CF 3 CO) N - (CF 3 SO 2), trimethyl allyl ammonium 2,2,2-trifluoro -N- (trifluoromethyl Sulfonyl) acetamide (CH ₃ ) ₃ N ⁺ (Allyl) (CF ₃ CO) N ⁻ (CF ₃ SO ₂ ), trimethylpropylammonium 2,2,2-trifluoro-N- (trifluoromethylsulfonyl) acetamide ( ^{_{CH 3) 3 N + (C}} 3 H 7) (CF 3 CO) N - (CF 3 SO 2), tetraethyl ammonium 2,2,2-trifluoro -N- (trifluoromethylsulfonyl) acetamide _{(C 2 ^{H 5) 4 N + (CF}} 3 CO) N - (CF 3 SO 2), triethyl methyl ammonium 2,2, - trifluoro -N- (trifluoromethylsulfonyl) acetamide _{(C 2 H 5) 3 N} + (CH 3) (CF 3 CO) N - (CF 3 SO 2), · 1- ethyl-3-methylimidazolium 2,2,2-trifluoro -N- (trifluoromethylsulfonyl) acetamide _{(C 2 H 5) (C} 3 H 3 N 2) + (CH 3) (CF 3 CO) N - (CF 3 SO 2) At least one selected from can be used.

On the other hand, as the lithium salt to be mixed with such room temperature molten salt, LiCF as above _{3 SO 3, LiC 4 F 9} SO 3, LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO ₂ ) ₂ and at least one selected from LiN (CF ₃ SO ₂ ) (COCF ₃ ) can be used.

  In the nonaqueous electrolyte secondary battery according to the present invention, a lithium-containing oxide can be used as a material for the positive electrode. And as this lithium containing oxide, what is generally used in the conventional nonaqueous electrolyte secondary battery can be used. As the positive electrode current collector in the positive electrode, an aluminum foil or a tantalum foil that can withstand a high potential can be used.

  In the non-aqueous electrolyte secondary battery according to the present invention, a carbon material such as graphite, which is a material that absorbs and releases lithium, can be used as the negative electrode material. In particular, in order to obtain a non-aqueous electrolyte secondary battery having a high energy density, as shown in Japanese Patent Application No. 2000-321200 and Japanese Patent Application No. 2000-321201 which are earlier applications of the present applicant, It is desirable to use large silicon. Moreover, when the thing which diffused copper to the silicon is used, the stress at the time of lithium occlusion will be relieved and cycling performance will improve. Moreover, copper foil can be used for the negative electrode current collector in this negative electrode. In particular, it is preferable to use a copper foil having a roughened surface obtained by electrolysis in order to improve adhesion to the negative electrode material.

  Hereinafter, the nonaqueous electrolyte secondary battery according to the present invention will be specifically described with reference to examples. In addition, the nonaqueous electrolyte secondary battery in this invention is not limited to what was shown in the following Example, It can implement by changing suitably in the range which does not change the summary.

(Example 1)
In Example 1, as the non-aqueous electrolyte, trimethyl octyl ammonium bis room temperature molten salt (trifluoromethylsulfonyl) imide ^{_{(CH 3) 3 N + (}} C 8 H 17) N - (CF 3 SO 2) 2 In addition, a nonaqueous electrolytic solution in which LiN (CF ₃ SO ₂ ) ₂ as a lithium salt was dissolved to a concentration of 1 mol / l was used. In addition, when the electrical conductivity of this non-aqueous electrolyte solution was measured, it was 0.111 mS / cm at 25 ° C. and had the electrical conductivity necessary for charging and discharging.

  As the negative electrode, an amorphous silicon thin film was formed by sputtering on a copper foil whose surface was subjected to electrolytic treatment, and formed into a size of 2 cm × 2 cm.

  As shown in FIG. 1, the nonaqueous electrolyte solution 14 is injected into the test cell container 10 and the negative electrode 11 is used as the working electrode, while the positive electrode 12 a and the reference electrode 13 serving as counter electrodes are used. A test cell of Example 1 was prepared using lithium metal.

Next, using the test cell thus prepared, the battery was charged at a current density of 0.025 mA / cm ² until the potential of the negative electrode 11 with respect to the reference electrode 13 became 0.0 V (vs. Li / Li ⁺ ). Discharge is performed until the potential of the negative electrode 11 with respect to the reference electrode 13 becomes 2.0 V (vs. Li / Li ⁺ ) at a current density of 0.025 mA / cm ² , and the negative electrode 11 is charged and discharged at the first cycle. The relationship between potential and capacitance was investigated, and the result is shown in FIG.

  As a result, in the test cell of Example 1, the charge capacity in the first cycle in the negative electrode 11 was 3346 mAh / g, and the discharge capacity in the first cycle was 2976 mAh / g, which is close to the theoretical capacity value of 4200 mAh / g. It was a value, and charging and discharging could be performed with a high capacity.

  Furthermore, using the test cell of this Example 1, charge and discharge were repeated as described above, and the charge capacity Qa (mAh / g) and the discharge capacity Qb (mAh / g) in each cycle were measured. And the charging / discharging efficiency (%) in each cycle was calculated | required with the following formula, The result was shown in FIG. In FIG. 3, the discharge capacity (mAh / g) in each cycle is indicated by a circle and a solid line, and the charge / discharge efficiency (%) in each cycle is indicated by a triangle and a broken line.

Charging / discharging efficiency (%) = (Qb / Qa) × 100

  As a result, in the test cell of Example 1 above, a high discharge capacity of about 2400 mAh / g was obtained even after the second cycle, and the charge / discharge efficiency was also very high.

(Example 2)
In Example 2, as the non-aqueous electrolyte, trimethylpropylammonium · bis room temperature molten salt (trifluoromethylsulfonyl) imide ^{_{(CH 3) 3 N + (}} C 3 H 7) N - (CF 3 SO 2) 2 In addition, a nonaqueous electrolytic solution in which LiN (CF ₃ SO ₂ ) ₂ as a lithium salt was dissolved to a concentration of 0.3 mol / l was used. In addition, when the electrical conductivity of this non-aqueous electrolyte solution was measured, it was 2.75 mS / cm at 25 ° C. and had the electrical conductivity necessary for charging and discharging.

  And the test cell of Example 2 was produced like the case of said Example 1 except using this non-aqueous electrolyte.

Next, using the test cell thus prepared, the battery was charged at a current density of 0.025 mA / cm ² until the potential of the negative electrode 11 with respect to the reference electrode 13 became 0.0 V (vs. Li / Li ⁺ ). Discharge is performed until the potential of the negative electrode 11 with respect to the reference electrode 13 becomes 2.0 V (vs. Li / Li ⁺ ) at a current density of 0.025 mA / cm ² , and the negative electrode 11 is charged and discharged at the first cycle. The relationship between potential and capacitance was examined, and the result is shown in FIG.

  As a result, in the test cell of Example 2, the first cycle charge capacity of the negative electrode 11 was 3370 mAh / g, and the first cycle discharge capacity was 2989 mAh / g, which is close to the theoretical capacity value of 4200 mAh / g. It was a value, and charging and discharging could be performed with a high capacity.

  Further, using the test cell of Example 2, charging and discharging were repeated as described above, and the charge capacity Qa (mAh / g) and the discharge capacity Qb (mAh / g) in each cycle were measured. The charge / discharge efficiency (%) in each cycle was determined in the same manner as in the test cell of Example 1 above, and the results are shown in FIG. In FIG. 5, the discharge capacity (mAh / g) in each cycle is indicated by a circle and a solid line, and the charge / discharge efficiency (%) in each cycle is indicated by a triangle and a broken line.

  As a result, in the test cell of Example 2, a high discharge capacity of 3183 mAh / g was obtained even in the ninth cycle, and the charge / discharge efficiency was also very high.

(Example 3)
In Example 3, as the non-aqueous electrolyte, trimethyl hexyl ammonium bis room temperature molten salt (trifluoromethylsulfonyl) imide ^{_{(CH 3) 3 N + (}} C 6 H 13) N - (CF 3 SO 2) 2 In addition, a nonaqueous electrolytic solution in which LiN (CF ₃ SO ₂ ) ₂ as a lithium salt was dissolved to a concentration of 0.5 mol / l was used.

  And the test cell of Example 3 was produced like the case of said Example 1 except using this non-aqueous electrolyte.

Next, using the test cell thus prepared, the battery was charged at a current density of 0.025 mA / cm ² until the potential of the negative electrode 11 with respect to the reference electrode 13 became 0.0 V (vs. Li / Li ⁺ ). Discharge is performed until the potential of the negative electrode 11 with respect to the reference electrode 13 becomes 2.0 V (vs. Li / Li ⁺ ) at a current density of 0.025 mA / cm ² , and the negative electrode 11 is charged and discharged at the first cycle. The relationship between potential and capacitance was examined, and the result is shown in FIG.

  As a result, in the test cell of Example 3, the charge capacity of the first cycle in the negative electrode 11 was 3133 mAh / g, and the discharge capacity of the first cycle was 2778 mAh / g, which is close to the theoretical capacity value of 4200 mAh / g. It was a value, and charging and discharging could be performed with a high capacity.

  Furthermore, using the test cell of Example 3, charging and discharging were repeated as described above, and the charge capacity Qa (mAh / g) and the discharge capacity Qb (mAh / g) in each cycle were measured. The charge / discharge efficiency (%) in each cycle was determined in the same manner as in the test cell of Example 1 above, and the results are shown in FIG. In FIG. 7, the discharge capacity (mAh / g) in each cycle is indicated by a circle and a solid line, and the charge / discharge efficiency (%) in each cycle is indicated by a triangle and a broken line.

  As a result, in the test cell of Example 3 described above, a high discharge capacity of 3411 mAh / g was obtained even in the ninth cycle, and the charge / discharge efficiency was also very high.

Example 4
In Example 4, as a nonaqueous electrolyte, triethylmethylammonium · 2,2,2-trifluoro-N- (trifluoromethylsulfonyl) acetamide (C ₂ H ₅ ) ₃ N ⁺ (CH ₃ ) _(CF 3 ^CO) N - the _(CF 3 sO _2), was used a LiN (CF ₃ sO _{2) 2} as a lithium salt was dissolved to a concentration of 0.5 mol / l non-aqueous electrolyte.

  And the test cell of Example 4 was produced like the case of said Example 1 except using this non-aqueous electrolyte.

Next, using the test cell thus prepared, the battery was charged at a current density of 0.025 mA / cm ² until the potential of the negative electrode 11 with respect to the reference electrode 13 became 0.0 V (vs. Li / Li ⁺ ). Discharge is performed until the potential of the negative electrode 11 with respect to the reference electrode 13 becomes 2.0 V (vs. Li / Li ⁺ ) at a current density of 0.025 mA / cm ² , and the negative electrode 11 is charged and discharged at the first cycle. The relationship between potential and capacitance was examined, and the result is shown in FIG.

  As a result, in the test cell of Example 4, the charge capacity at the first cycle in the negative electrode 11 was 10504 mAh / g, and the discharge capacity at the first cycle was 1376 mAh / g, and charging / discharging could be performed.

(Example 5)
In Example 5, 1-ethyl-3-methylimidazolium · 2,2,2-trifluoro-N- (trifluoromethylsulfonyl) acetamide (C ₂ H ₅ ), which is a room temperature molten salt, is used as the nonaqueous electrolyte. (C ₃ H ₃ N ₂ ) ⁺ (CH ₃ ) (CF ₃ CO) N ⁻ (CF ₃ SO ₂ ) and LiN (CF ₃ SO ₂ ) ₂ as a lithium salt to a concentration of 0.5 mol / l A nonaqueous electrolytic solution dissolved in was used.

  And the test cell of Example 5 was produced like the case of said Example 1 except using this non-aqueous electrolyte.

Next, using the test cell thus prepared, the battery was charged at a current density of 0.025 mA / cm ² until the potential of the negative electrode 11 with respect to the reference electrode 13 became 0.0 V (vs. Li / Li ⁺ ). Discharge is performed until the potential of the negative electrode 11 with respect to the reference electrode 13 becomes 2.0 V (vs. Li / Li ⁺ ) at a current density of 0.025 mA / cm ² , and the negative electrode 11 is charged and discharged at the first cycle. The relationship between the potential and the capacitance was examined, and the result is shown in FIG.

  As a result, in the test cell of Example 5, the charge capacity in the first cycle in the negative electrode 11 was 16585 mAh / g, and the discharge capacity in the first cycle was 1537 mAh / g, and charging / discharging could be performed.

Then, from the results of Examples 1 to Example 5, a negative electrode 11 with silicon, trimethyl octyl ammonium bis (trifluoromethylsulfonyl) imide is room temperature molten salt ^{_{(CH 3) 3 N + (}} C 8 _{^{H 17) N - (CF 3}} SO 2) 2 and, trimethylpropylammonium · bis (trifluoromethylsulfonyl) imide _{^{(CH 3) 3 N + (}} C 3 H 7) N - (CF 3 SO 2) 2 and, trimethylhexyl ammonium bis (trifluoromethylsulfonyl) imide ^{_{(CH 3) 3 N + (}} C 6 H 13) N - (CF 3 SO 2) 2 and, triethyl methyl ammonium 2,2,2 -N - (trifluoromethylsulfonyl) acetamide _{(C 2 H 5) 3 N} + (CH 3) (CF 3 CO) N - ( F ₃ SO ₂₎ and 1-ethyl-3- methylimidazolium 2,2,2-trifluoro -N- (trifluoromethylsulfonyl) acetamide _{(C 2 H 5) (C} 3 H 3 N 2) + ^{_{(CH 3) (CF 3 CO}} ) N - (CF 3 SO 2) in a non-aqueous electrolyte secondary battery using a nonaqueous electrolytic solution 14 obtained by dissolving LiN (CF ₃ SO _{2) 2} lithium salt Even in this case, it is considered that charging and discharging can be performed appropriately.

(Example 6)
In Example 6, using the LiCoO ₂ powder material of the positive electrode, the LiCoO ₂ powder and a binder polyvinylidene fluoride and 95: as a weight ratio of 5, polyvinylidene fluoride to LiCoO ₂ powder A 5% by weight N-methyl-2-pyrrolidone solution was added, and this was ground for 30 minutes with a cracking machine to prepare a slurry. This slurry was applied to both sides of an aluminum foil having a thickness of 20 μm by the doctor blade method, This was dried to produce a positive electrode.

As the non-aqueous electrolyte, as in Example 1 above, trimethyloctylammonium bis (trifluoromethylsulfonyl) imide (CH ₃ ) ₃ N ⁺ (C ₈ H ₁₇ ) N ⁻ (CF ₃ SO ₂₎ was used LiN (CF ₃ sO _{2) 2} the non-aqueous electrolytic solution obtained by dissolving to a concentration of 1 mol / l to _2.

  Then, as shown in FIG. 10, the nonaqueous electrolyte solution 14 is injected into the test cell container 10 and the positive electrode 12 is used as the working electrode, while the negative electrode 11a and the reference electrode 13 serving as counter electrodes are used. A test cell of Example 6 was prepared using lithium metal.

Next, using the test cell thus prepared, after charging at a current density of 0.025 mA / cm ² until the potential of the positive electrode 12 with respect to the reference electrode 13 becomes 4.3 V (vs. Li / Li ⁺ ), Discharging is performed until the potential of the positive electrode 12 with respect to the reference electrode 13 reaches 2.75 V (vs. Li / Li ⁺ ) at a current density of 0.025 mA / cm ² , and the potential of the positive electrode 12 during initial charging and during initial discharging. FIG. 11 shows the results of the investigation of the relationship between the capacity and the capacity.

  As a result, in the test cell of Example 6, the positive electrode 12 had an initial charge capacity of 29.8 mAh / g and an initial discharge capacity of 25.8 mAh / g, and was able to be charged and discharged.

(Example 7)
In Example 7, a positive electrode in which a LiCoO ₂ layer was formed on an aluminum foil by sputtering was used.

As the non-aqueous electrolyte, as in the case of Example 2, the room temperature molten salt trimethylpropylammonium bis (trifluoromethylsulfonyl) imide (CH ₃ ) ₃ N ⁺ (C ₃ H ₇ ) N ^- the _(CF 3 _{sO 2) 2,} was used LiN (CF ₃ sO _{2) 2} was dissolved to a concentration of 0.3 mol / l aqueous electrolyte solution as the lithium salt.

  As in the case of Example 6, the nonaqueous electrolyte solution 14 is injected into the test cell container 10, and the positive electrode 12 is used as the working electrode, while the negative electrode 11a serving as the counter electrode and A test cell of Example 7 was prepared using lithium metal for each reference electrode 13.

Next, using the test cell thus produced, after charging until the potential of the positive electrode 12 with respect to the reference electrode 13 becomes 4.2 V (vs. Li / Li ⁺ ) at a current density of 0.025 mA / cm ² , Discharging is performed until the potential of the positive electrode 12 with respect to the reference electrode 13 reaches 2.0 V (vs. Li / Li ⁺ ) at a current density of 0.025 mA / cm ² , and the potential of the positive electrode 12 during initial charging and during initial discharging. FIG. 12 shows the result of the investigation of the relationship between the capacity and the capacity.

  As a result, in the test cell of Example 7, the positive electrode 12 had an initial charge capacity of 104 mAh / g and an initial discharge capacity of 104 mAh / g, and was able to be charged and discharged.

  Further, using the test cell of Example 7, charging and discharging were repeated as described above, and the charge capacity Qa (mAh / g) and the discharge capacity Qb (mAh / g) in each cycle were measured. The charge / discharge efficiency (%) in each cycle was determined in the same manner as in the case of the test cell of Example 1, and the results are shown in FIG. In FIG. 13, the discharge capacity (mAh / g) in each cycle is indicated by a circle and a solid line, and the charge / discharge efficiency (%) in each cycle is indicated by a triangle and a broken line.

  As a result, in the test cell of Example 7 described above, a high discharge capacity of 95 mAh / g was obtained even in the seventh cycle, and the charge / discharge efficiency was also very high.

From the results of Examples 6 and 7, the positive electrode using LiCoO ₂ and the room temperature molten salt trimethyloctylammonium bis (trifluoromethylsulfonyl) imide (CH ₃ ) ₃ N ⁺ (C _{8 ^{H 17) N - (CF 3}} SO 2) 2 and, trimethylpropylammonium · bis (trifluoromethylsulfonyl) imide ^{_{(CH 3) 3 N + (}} C 3 H 7) N - ( lithium CF 3 _{SO 2) 2} Even when a non-aqueous electrolyte secondary battery is produced using a non-aqueous electrolyte solution 14 in which the salt LiN (CF ₃ SO ₂ ) ₂ is dissolved, it is considered that charging and discharging can be performed appropriately.

Further, when a non-aqueous electrolyte in which a lithium salt LiN (CF ₃ SO ₂ ) ₂ is dissolved in a room temperature molten salt as shown in Examples 1 to 7 above, abnormal operation such as overcharging is performed. Even at times, the non-aqueous electrolyte does not decompose or burn.

  As described above in detail, in the non-aqueous electrolyte secondary battery according to the present invention, since the non-aqueous electrolyte containing a room temperature molten salt having a melting point of 60 ° C. or less and a lithium salt is used, the lithium salt is used as a positive electrode. It is possible to charge and discharge by moving between the negative electrode and non-aqueous electrolyte will not be decomposed or burned even during abnormal operation such as overcharge, and no protective circuit etc. are provided Can now be used safely.

It is a schematic explanatory drawing of the test cell produced in Example 1- Example 5 of this invention. It is the figure which showed the relationship between the electric potential and capacity | capacitance of the negative electrode with respect to the reference electrode at the time of charge of 1st cycle and the discharge at the time of charging / discharging the test cell of Example 1. FIG. It is the figure which showed the discharge capacity and charging / discharging efficiency of each cycle when the test cell of Example 1 was repeatedly charged and discharged. It is the figure which showed the relationship between the electric potential and capacity | capacitance of the negative electrode with respect to the reference electrode at the time of charge of 1st cycle and the discharge in the case of charging / discharging the test cell of Example 2. FIG. It is the figure which showed the discharge capacity and charging / discharging efficiency of each cycle when the test cell of Example 2 was repeatedly charged and discharged. It is the figure which showed the relationship between the electric potential of a negative electrode with respect to the reference electrode at the time of charge of 1st cycle, and the time of discharge, and a capacity | capacitance at the time of charging / discharging the test cell of Example 3. FIG. It is the figure which showed the discharge capacity and charging / discharging efficiency of each cycle when the test cell of Example 3 was repeatedly charged and discharged. It is the figure which showed the relationship between the electric potential of a negative electrode with respect to the reference electrode at the time of charge of 1st cycle, and the time of discharge, and a capacity | capacitance at the time of charging / discharging the test cell of Example 4. FIG. It is the figure which showed the relationship between the electric potential of the negative electrode with respect to the reference electrode at the time of charge of 1st cycle, and the discharge at the time of charging / discharging the test cell of Example 5, and a capacity | capacitance. It is a schematic explanatory drawing of the test cell produced in Example 6 and Example 7 of this invention. It is the figure which showed the relationship between the electric potential and capacity | capacitance of the positive electrode with respect to the reference electrode at the time of an initial stage charge at the time of an initial stage charge at the time of charging / discharging the test cell of Example 6. FIG. It is the figure which showed the relationship between the electric potential and capacity | capacitance of the positive electrode with respect to the reference electrode at the time of initial charge at the time of charging / discharging the test cell of Example 7, and the initial discharge. It is the figure which showed the discharge capacity and charging / discharging efficiency of each cycle when the test cell of Example 7 was repeatedly charged and discharged.

Explanation of symbols

10 Test cell container
11,11a Negative electrode
12,12a positive electrode
13 Reference pole
14 Non-aqueous electrolyte

Claims (3)

In a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, a negative electrode having a roughened copper foil and a silicon thin film formed thereon is used, and a melting point of 60 ° C. or lower is used. Room temperature molten salt composed of quaternary ammonium salt, LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) Using a nonaqueous electrolyte containing at least one lithium salt selected from (COCF ₃ ) , the above-mentioned room temperature molten salt consisting of a quaternary ammonium salt having a melting point of 60 ° C. or lower is added to trimethylpropylammonium bis (tri Fluoromethylsulfonyl) imide, trimethyloctylammonium bis (trifluoromethylsulfonyl) imide, trimethylallylammonium bis (trifluoromethyl) Sulfonyl) imide, trimethylhexylammonium bis (trifluoromethylsulfonyl) imide, trimethylethylammonium 2,2,2-trifluoro-N- (trifluoromethylsulfonyl) acetamide, trimethylallylammonium 2,2,2- Trifluoro-N- (trifluoromethylsulfonyl) acetamide, trimethylpropylammonium 2,2,2-trifluoro-N- (trifluoromethylsulfonyl) acetamide, tetraethylammonium 2,2,2-trifluoro-N- (trifluoromethylsulfonyl) acetamide methyl ammonium 2,2,2-trifluoro -N- birds for using at least one member selected from (trifluoromethylsulfonyl) acetamide Non-aqueous electrolyte secondary battery according to symptoms. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein a lithium-containing oxide is used for the positive electrode. 3. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein a copper foil obtained by electrolysis is used as the copper foil.

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